L3: Antigens and Antibodies Flashcards Preview

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Flashcards in L3: Antigens and Antibodies Deck (22):

List and describe the features on the adaptive immune system in our bodies

1.) Specificity: specificity of each lymphocyte against one epitope
2.) Immunologic memory: faster and more vigorous response upon re-exposure to antigen as a result of memory cells, which has more sensitivity to antigen
3.) Diversity: numerous pre-existing antigen-specific lymphocytes
4.) Self-regulation: removal of antigen should mean no further immunologic stimulation, activated lymphocytes die, regulation
5.) Discrimination of self v non-self: adaptive responses only against foreign antigens, not self as self-specific immune cells are destroyed or regulated


What is immunogenicity?

- properties that promote immune responses
- adjuvants cause increased immunogenicity


What is antigenicity?

- properties that allow a substance to react with an antibody


What are haptens?

- small molecules that cannot induce antibody formation by themselves, they require carrier molecule to induce antibodies
- eg. Penicillin:albumin = antibody response


Important features of immunogen

- Size: >10000 MW
- Internal complexity: more complex, more immunogenic
- Degradability
- Foreigness
- Accessibility


Different types of antigen conformations seen by antibody

1.) Conformational determinants: only native conformation recognized, not denatured
2.) Linear determinants: recognized in both native and linear form (from denaturation or processing)
3.) Neoantigenic determinants: determinant not present in native form, requires proteolysis


What types of determinants/antigen conformations will T cells only recognize?

- Only linear determinants, resulting from processing


Of all the types of antigens (protein, lipoprotein, etc.) available, what is the most immunogenic?

- Protein


What immunoglobulins are expressed on naïve B cells?

- IgM and IgD


What immunoglobulins to mast cells and basophils have Fc receptors for?

- They have Fc-epsilon receptors for IgE


Difference between monoclonal and polyclonal antiserum?

- Polyclonal = abs that bind to more than one particular antigen
- Monoclonal = abs that bind to one specific antigen


What does antibody titer refer to?

- Reciprocal of last dilution of antiserum that still yields a demonstrable antibody binding reaction.
- Example: if reactions seen in 1:8, 1:16, 1:32 and 1:64, but not in 1:128, then titer is 64. The higher this number, the larger the concentration of antibody to a specific antigen is present


In what fraction of serum proteins are most antibodies found?

- Gamma fraction


Describe structure of antibody

- 2 identical heavy and 2 identical light chains
- Heavy chains connected by disulfide bonds
- Light chains connected to heavy chains by disulide bonds
- Each of the chains consists of constant (C) and variable (V) regions. Variable regions subdivided into hypervariable (fingertips) and framework (fingers) regions
- Antigen binding site = VL and VH seen on both arms
- G, A and D Igs have hinge regions, which provide flexibility to antibody arms
- Except for D Igs, have secretory and membrane form


What is a J-chain?

- J-chains are found in secretory forms if IgM and IgA and allow formation of pentamers of IgM or dimers/trimers of IgA


What does papain and pepsin digestion of antibody result in?

- Pepsin: single fragment of arms bound together (Fab2) + no surviving Fc fragment
- Papain: two arm fragments (Fab’s) + one Fc fragment


Classification of antibodies isotypes. Describe, list function

1.) IgG: has sub-classes 1-4, most abundant, activates complement, 1 and 3 can opsonize using Fc-gamma receptor on phagocytes, coats tumor or virally-infected cells for ADCC facilitation with NK cells, crosses placenta, in mother’s milk, predominates in secondary immune response

2.) IgM: exists in pentamer with J-chain, best activator of complement, predominates in primary immune response

3.) IgA: has sub-classes 1-2, exists in dimer/trimer with J-chain in secretions but monomeric in secretions (when secreted, coupled to secretory piece to protect from proteolytic enzymes), mediator of mucosal immunity, present in tears/saliva/colostrum and milk, participates in eosinophil-mediated ADCC of certain parasitic infections (worms)

4.) IgD: always membrane bound, primarily on naïve B cells, important in transduction of signals across plasma membrane to result in antigen-driven B cell activation

5.) IgE: participates in eosinophil-mediated ADCC of certain parasitic infections (worms), binds to Fc-epsilon receptors on basophils and mast cells to mediate allergies and anaphylaxis


Which antibody isotype is the best activator of complement?

- IgM


What is the main antibody isotype in a primary immune response? Secondary?

- Primary: IgM
- Secondary: IgG


Avidity vs affinity

- Avidity: overall strength of antibody attachment taking into account how many antigen combining sites antibody has bound
- Affinity: strength of binding for antigen of one antigen combining site (on arm)


Which antibody isotype has greater affinity? Avidity?

- IgG has greater affinity
- IgM has greater avidity due to pentameric form it primarily exists in


What is allotype? Idiotype?

- Allotype: differences in constant region of antibodies of the same isotype
- Idiotype: collection of hypervariable regions contributed by H and L chains that form the antigen-binding site